It sounds like that might be better for a statically-typed language where you might need specific types in the data file. But I would argue that not only is it overkill in a dynamically-typed language, it's bad. We're talking about data here. There's no reason to couple it to data types in your code.
Plus, serialization to JSON in a dynamically-typed language is pretty much automagic compared to what you have to do with XML.